1. Field of the Invention
This present invention relates to an apparatus and method for applying heat to tissue within a body cavity for therapeutic purposes.
2. Description of the Prior Art
As a natural consequence of aging and other biochemical factors, atherosclerotic obstructions consisting of fatty deposits, fibrous tissue and eventually calcium, tend to form on the vessel walls of the human coronary, peripheral and cerebral vasculature. As this accumulation progresses, the lumen of the artery is narrowed (or, sometimes completely blocked), restricting or preventing adequate supply of oxygenated blood to supply the muscles of the heart or legs.
The state of inadequate oxygenation, known as "ischemia," when it occurs in the coronary arteries, results in abnormalities of the biochemical, electrical and mechanical functions of the heart. The clinical manifestation of this condition may include angina pectoris, acute myocardial infarction or ventricular arrhythmia that can lead to sudden death.
In the peripheral arteries, the ischemia condition commonly occurs with exercise and is termed "intermittent claudication," i.e., the pain that occurs in a muscle with inadequate blood supply that is stressed by exercise. Pain may also occur at rest and may be continuous in the toes and foot. Occasionally numbness or paresthesias may be present. Ulceration and gangrene of the toes and distal foot are common when the disease reaches advanced stages. Amputation is sometimes required.
Many therapeutic interventions have been available to treat coronary, peripheral and cerebral vascular disease. Drugs that dilate the vessel and lower blood viscosity are prescribed to prevent or lessen an ischemic attack.
The introduction of polyvinyl balloon tipped catheters marked the beginning of a new era in revascularization techniques. These catheters are threaded through the vasculature, via a percutaneous incision, to the site of occlusion. The balloon is then inflated using an accessory device located outside the body. As the balloon inflates, the lumen of the artery is increased to allow for greater blood flow resulting in the alleviation of symptoms.
Bypass surgery is frequently prescribed. Grafting a healthy vessel around the diseased one provides a new connection for blood flow to the portion of the artery that is distal to the diseased section.
More recent treatment techniques have focused on the use of high energy laser light pulses conducted through a fiber optic bundle to remove atherosclerotic deposits.
The use of laser energy has also been used to heat a metal tipped catheter which then melts or dissolves the plaque. Lasers, however, are complex, relatively large, expensive and very inefficient. The use of lasers for removing plaque deposits is still in the formative stages.
In addition to the use of expandable balloons and lasers, it has been suggested in U.S. Pat. No. 4,643,186 that the plaque deposits be radiated with microwave energy via a transmission line inserted through the affected artery. Such a technique has several inherent problems. For example, the plaque will provide a variable load to the microwave source depending upon the moisture content of the plaque. Such a variable load makes it difficult to control the amount of power applied to the plaque to vaporize or otherwise remove the same without creating a risk of damaging the vessel wall.
There is a need for a simple and effective apparatus for reducing the occlusive effect of plaque deposits within blood vessels.